Let c represent the capacity of the larger bottle. Then the capacity of the smaller bottle is (1/2)c. Since the larger bottle is 2/3 full, it contains (2/3)c mayo. The smaller bottle contains (1/3)(1/2)c = (1/6)c mayo. When you pour the smaller bottle into the larger one, you get (2/3)c + (1/6)c = (5/6)c mayo. Therefore, the larger bottle is 5/6 full of mayo.